A blade system is a server chassis housing multiple, modular electronic circuit boards known as server blades or blades. The server chassis or blade enclosure, which can hold multiple blades, provides services such as power, cooling, networking, various interconnects and management. Each blade can be composed of more than one processor, memory, integrated network controllers, and other input/output ports, and each blade may also be configured with local drives and can connect to a storage pool facilitated by a network-attached storage, Fiber Channel, or iSCSI storage-area network.
FIG. 1 shows a blade system 100 composed of eight blades 102-109 mounted in a blade enclosure or chassis 110. Each blade can be electronically coupled to one or both switch fabrics 112 and 114 that provide input/output connectivity between the blades. However, the switch fabrics typically do not support coherent memory traffic. For example, in multi-processor systems, such as a blade system, there may be two or more processors in need of processing the same set of data at the same time. Provided none of the processors updates the data, the processors can share the data indefinitely. On the other hand, as soon as one processor updates the data, the other processors will be working on out-of-date data. As a result, data is often stored in memory partitions and limited to processing by one blade at a time. This makes it difficult to develop blades with different and specific capabilities, such as compute, memory, storage, and input/output, and link them together to meet the specific needs of customers and applications. Recently, blade systems have been developed with coherent memory switches disposed between blades and between blade systems. However, the bandwidth needed causes a substantial increase in the cost of these coherent switches, and the cables needed to interconnect blade systems are large and bulky. These switches add multiple hops of latency between blade systems, and cable management concerns can force a reduction in bisection bandwidth, which impacts performance. What is desired is a blade system providing high-speed, high-bandwidth, and low-latency communication across any group of blades that are physically contiguous.